Measurement of the electrical conductivity of different tissues of fish Maja Walz
Animal welfare becomes increasingly important when animals are slaughtered. Thus, many animals are electrically stunned before slaughter. Computer simulations using finite element analysis can help to improve procedures and prevent animal suffering.
To simulate the current flow and current density in the head of an animal during electric stunning, the electrical conductivity of the existing tissues is required. However, these data are currently only available for mammals (including humans) and not for fish.
Therefore, previous computer simulations of electric stunning have used the electrical conductivities of human tissues and the tissues of other mammals. However, fish and mammalian tissues are different in their composition, so that the electrical conductivities of fish tissues can be used to significantly improve the accuracy of computer simulations.
In order to measure the electrical conductivity of fish tissues, this dissertation developed a measurement setup based on the 4-point method. A multi-channel ECG, which was developed in the context of a master thesis at the TU Braunschweig, was used as a power source (Gehring 2015). For reliable and reproducible contacting of the tissue a special electrode probe with platinum-iridium electrodes was developed.
The electrodes were embedded with equal spacing in a plastic platelet, which they protrude by 1 mm each. When the electrodes penetrate into the biological tissue, the pressure force is distributed over the surface of the plastic platelet instead of over the
electrode tips, so that it has no influence on the measurement of the electrical resistance. The validation of this measurement setup showed that the electrical resistance of biological tissue could be measured reliably and reproducibly.
Tissue samples of the edible fish carp, trout and African catfish were examined. The focus was on the tissue types found on the head of a fish (muscle, skin, bone, eyes, fat, brain).
In total, about 2000 measured values were evaluated by calculating the corresponding electrical conductivities from the measured electrical resistances. For each of the above-mentioned biological tissues, the mean value for the electrical conductivity including the 95 % confidence interval was determined. In future computer simulations, these conductivity values will be used to optimize the parameters for electric stunning before slaughter.
The electrical conductivity values of fish tissues show varying degrees of deviation from the corresponding values for human tissue. On the one hand, the electrical conductivity of fish skin, for example, is up to 20 times greater than that of human skin.
On the other hand, the electrical conductivity of brain tissue, for example, is 0.07 to 0.10 S/m in fish and 0.08 S/m in humans. In addition, differences were also found between the investigated fish species, so that separate computer simulations have to be carried out for each fish species. For example, the electrical conductivity of the muscles of trout is about 0.3 S/m, while the muscles of the other two investigated fish species have an electrical conductivity of only about 0.1 S/m.
To refine and validate the measurement protocols, the influence of the parameters temperature and time on the measurement results was investigated. This also served as an estimation of the extent to which the ex vivo measured values deviate from the in vivo values that are not accessible and which parameters have to be taken into account for electrical stunning. For muscle tissue, for example, it was found that the fluctuations due to the temperature dependence of the electrical resistance are negligible compared to the individual differences in electrical resistance of the different tissue samples. Furthermore, it could be shown within the scope of this dissertation that the electrical resistance changes to different degrees during the aging process of the tissue samples. While the electrical resistance of muscle tissue decreases over time, the electrical resistance of skin and fascial tissue did not show a uniform dependence on time. Therefore, it is recommended to perform the measurements of the electrical resistance as soon as possible after the death of the fish.
The electrical conductivity of different fish tissues was determined for the first time in this dissertation. These results serve to optimize the computer simulations.
Furthermore, the developed measurement setup can be used for further measurements of the electrical resistance of animal tissues.
8 Literaturverzeichnis
(Destatis), S. B. (2019). "Land und Forstwirtschaft, Fischerei, Erzeugung in Aquakulturbetrieben." Fachserie 3 Reihe 4.6: S. 4.
Baumgärtner, W. and A. D. Gruber (2015). Spezielle Pathologie für die Tiermedizin, Georg Thieme Verlag: 345.
Behrendt, N. (2005). Modulation der Muzinproduktion der Schleimhaut des Karpfens (Cyprinus carpio) unter Kontamination des Aquarienwassers mit Aeromonas hydrophila, Verlag nicht ermittelbar.
Bundeszentrum für Ernährung (2018). Ernährung/Lebensmittel/Nachhaltiger Konsum.
Dunajski, E. (1980). "Texture of fish muscle." Journal of Texture Studies 10(4): 301-318.
EFSA, E. F. S. A. (2004). "Opinion of the Scientific Panel on Animal Health and Welfare (AHAW) on a request from the Commission related to welfare aspects of the main systems of stunning and killing the main commercial species of animals." EFSA Journal 2(7).
Egger, R. and H. Schoberwalter (2017). Dynamische Faszien, Springer: 3-16.
European Food Safety Authority, E. (2009). "Species‐specific welfare aspects of the main systems of stunning and killing of farmed Carp." EFSA Journal 7(4).
FAO. (2020). The State of World Fisheries and Aquaculture (SOFIA). Rome, Italy, FAO.
Fiedler, K. (1991). Lehrbuch der speziellen Zoologie. Band II: Wirbeltiere, Teil 2:
Fische, Gustav Fischer Verlag, Jena: 21-25.
Fisch-Informationszentrum (2020). "Daten und Fakten."
Gabriel, C., et al. (1996). "The dielectric properties of biological tissues: I. Literature survey." Phys Med Biol 41(11): 2231-2249.
Gabriel, S., et al. (1996). "The dielectric properties of biological tissues: II.
Measurements in the frequency range 10 Hz to 20 GHz." Phys Med Biol 41(11): 2251-2269.
Gabriel, S., et al. (1996). "The dielectric properties of biological tissues: III. Parametric models for the dielectric spectrum of tissues." Phys Med Biol 41(11): 2271-2293.
Geddes, L. A. and R. Roeder (2003). "Criteria for the Selection of Materials for Implanted Electrodes." Annals of Biomedical Engineering 31(7): 879-890.
Gehring, S. (2015). "Vielkanal-EKG mit integrierter Hautwiderstandsmessung."
Masterarbeit, Institut für Elektrische Messtechnik und Grundlagen der Elektrotechnik, TU Braunschweig
Guerra, R., et al. (2006). "Stratum adiposum, a special structure of the African catfish skin (Clarias gariepinus, Burchell 1822)." Anatomia, histologia, embryologia 35(3):
144-146.
Hörnig (2017). "Simulation der Betäubung Afrikanischer Welse mit Hilfe der Finite-Elemente-Analyse
(FEA)."
Iger, Y. and M. Abraham (1990). "The process of skin healing in experimentally wounded carp." Journal of Fish Biology 36(3): 421-437.
Jung-Schroers, D. V. (2017). "Empfehlungen zur Betäubung und Schlachtung von Regenbogenforellen." Modell-und Demonstrationsvorhaben (MuD) Tierschutz.
Keshtkar, A. and A. Keshtkar (2008). "The effect of applied pressure on the electrical impedance of the bladder tissue using small and large probes." Journal of Medical Engineering & Technology 32(6): 505-511.
Knoblauch, C. (2015). "Impedanzspektroskopie–Ein Überblick von der Theorie bis zur Anwendung."
Lambooij, E., et al. (2004). "Head-only electrical stunning and bleeding of African catfish (Clarias gariepinus): assessment of loss of consciousness." Animal welfare 13(1): 71-76.
Lambooij, E., et al. (2006). "Assessment of electrical stunning in fresh water of African Catfish (Clarias gariepinus) and chilling in ice water for loss of consciousness and sensibility." Aquaculture 254(1): 388-395.
Law, E. U. (2009). "Council Regulation (EC) No 1099/2009 of 24 September 2009 on the protection of animals at the time of killing (Text with EEA relevance)." Official Journal of the European Union https://eur-lex.europa.eu/eli/reg/2009/1099/oj.
Martinsen, O. G. and S. Grimnes (2011). Bioimpedance and Bioelectricity Basics.
123Library, Academic Press: 85-87; 180-184.
Meßlinger, K. (2002). "Physiologie und Pathophysiologie der Schmerzentstehung."
Manuelle Medizin 40(1): 13-21.
Niedersachsen, L. (2011).
"https://www.lwk-niedersachsen.de/index.cfm/portal/tier/nav/231/article/6971.html."
PAL Aquakultur, G. (2016). "Informationen zur Produktion von afrikanischem Wels in Warmwasserkreislaufanlagen (Aquakultur). ." S. 2-5.
Raith, W. (2008). Elektromagnetismus, Walter de Gruyter. 2: 806.
Robb, D. H. F., et al. (2002). "Electrical stunning of rainbow trout (Oncorhynchus mykiss): factors that affect stun duration." Aquaculture 205(3): 359-371.
Rommel, K. (1980). Die kleine Leitfähigkeits-Fibel: Einführung in die Konduktometrie für Praktiker, WTW: 7.
Rose, J. D., et al. (2014). "Can fish really feel pain?" Fish and Fisheries 15(1): 97-133.
Ruge, I. and H. Mader (2013). Halbleiter-Technologie, Springer Berlin Heidelberg. 4:
187-192.
Sattari, A., et al. (2010). "Industrial dry electro-stunning followed by chilling and decapitation as a slaughter method in Claresse®(Heteroclarias sp.) and African catfish (Clarias gariepinus)." Aquaculture 302(1-2): 100-105.
Schmid, G., et al. (2003). "Dielectric properties of human brain tissue measured less than 10 h postmortem at frequencies from 800 to 2450 MHz." Bioelectromagnetics 24(6): 423-430.
Schrüfer, E., et al. (2014). Elektrische Messtechnik: Messung elektrischer und nichtelektrischer Größen, Carl Hanser Verlag GmbH Co KG: 182.
Schwan, H. P. (1992). "Linear and nonlinear electrode polarization and biological materials." Annals of Biomedical Engineering 20(3): 269-288.
Stamer, A. (2009). "Betäubungs-und Schlachtmethoden für Speisefische."
Storch, V. and U. Welsch (2014). Kükenthal-Zoologisches Praktikum, Springer-Verlag:
356.
Tierschutzbund, D. (2015). "Töten von Fischen aus Aquakulturen vom November 2015."
Verbraucherschutz, B. d. J. u. f. "TierSchG https://www.gesetze-im-internet.de/tierschg/index.html."
von Engelhardt, W. and G. Breves (2005). Physiologie der Haustiere. Schweizer Archiv für Tierheilkunde. 147: 654.
9 Anhang
Tab. 3: Elektrische Leitfähigkeit verschiedener Gewebe aus Forellen.
Gewebe n σ [S/m] Zeitpunkt der
n – Anzahl der Proben, ϑ – mittlere Temperatur der Proben, Z – mittlerer Zeitpunkt der Messungen, σ – elektrische Leitfähigkeit.
Tab. 4: Elektrische Leitfähigkeit verschiedener Gewebe aus Karpfen.
Tab. 5: Elektrische Leitfähigkeit verschiedenen Gewebe aus afrikanischen Welsen.